The invention relates to detecting and measuring the quality and sharpness of radiation images and to utilizing the resulting information. It finds particular utility in automatic focusing of cameras and projectors, in range finding, and the like.
In cameras and projectors, it is essential to properly focus an image in order to avoid loss of pictorial information. Focusing is usually manual, by adjusting the distance between the objective lens and the film in cameras, and by adjusting the distance between the projection lens and the image carrier in projectors. In some cameras focusing is eliminated by the use of the so-called universal focus lenses which do not require focusing adjustments within the distance range usually encountered by the amateur photographer. Such lenses, however, are a compromise between eliminating focusing problems and providing an image of optimum quality, and are therefore not satisfactory under all conditions. Attempts have been made therefore to provide various devices for automatically focusing conventional objective lenses, and similar attempts have been made for automatically focusing projection lenses. Some such devices rely on triangulation and measure the angle between the lines to a subject from two spaced-apart points on the camera (Pagel U.S. Pat. No. 3,442,193). Others rely on observing minute differences in the output of certain photocells between uniform and nonuniform distributions of light over their surface (Harvey U.S. Pat. No. 3,653,762). Still others rely on measuring the phase difference between different rays reflected from the subject to be photographed (Odone et al. U.S. Pat. No. 3,652,160). Still others rely on measuring the relative light intensity difference between two or more points of an image (Genahr U.S. Pat. No. 3,532,045 and Leitz U.S. Pat. No. 3,529,528). A survey of certain prior art focusing techniques can be found in Shin, I., Autofocus Camera, RADC Final Techn. Report TR-72-244, Oct. 1972, Defense Documentation Center No. AD-905-565L. In projectors, one automatic focusing device scans a line of the projected image and uses the count of certain transitions between light and dark as a measuring of focusing (Fenner U.S. Pat. No. 3,705,765).
While it is highly desirable to provide an indication of the sharpness of images, automatic focusing of cameras and projectors and automatic range finding, for various reasons having to do with complexity, reliability and effectiveness, no commercial devices of this type have enjoyed unqualified success. There is still a need for a way to detect and measure the sharpness and quality of images simply and reliably, and to utilize the result for accurate manual or fully automatic focusing and range finding, for modifications of optical systems, and the like.